Cell & Molecular Biology Program Event
Dr. Christian Jordan
Cellular and Molecular Biology
University of Vermont
DNA Repair, Replication, and Recombination in Bacteriophage T4
Tuesday November 13th, 2012
Dda, one of three helicases encoded by bacteriophage T4, has been well-characterized biochemically but its biological role remains unclear. It is thought to be involved in origin dependent replication, anti-recombination, and recombination repair. The Gp32 protein of bacteriophage T4 plays critical roles in DNA replication, recombination, and repair by coordinating protein components of the replication fork and by stabilizing ssDNA. Previous work demonstrated that stimulation of DNA synthesis by Dda helicase appears to require direct Gp32-Dda protein-protein interactions and that Gp32 and Dda form a tight complex in the absence of ssDNA. Here we characterize the effects of this complex through changes in the duplex DNA unwinding and ATPase activities of Dda helicase in the presence of different variants of Gp32 and different DNA repair and replication intermediate structures. Results show that complex formation can be enhancing or inhibitory, depending on the Gp32 domain seen by Dda, and that the effect requires a minimum DNA unwinding length in order to be observed. These and other results indicate that Gp32 affects helicase assembly and translocation on ssDNA that forms on replication and recombination intermediates, which suggest a mechanism for the regulation of recombination-dependent DNA replication. Helicase activation results in increased turnover of ATP, suggesting a higher rate of ATPase-driven translocation. Evidence suggests that Dda may overcome protein blocks on DNA only in the presence of a Gp32 variant, a capability that could be important for the restart of stalled replication forks.